U.S. patent application number 12/149099 was filed with the patent office on 2008-10-30 for weighing scale.
This patent application is currently assigned to TANITA Corporation. Invention is credited to Masayuki Kenmochi.
Application Number | 20080264141 12/149099 |
Document ID | / |
Family ID | 39560891 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264141 |
Kind Code |
A1 |
Kenmochi; Masayuki |
October 30, 2008 |
Weighing scale
Abstract
A weighing scale includes a platform on which an object to be
weighed is placed, a weight measurer for outputting weight data
indicating an apparent weight value of the object to be weighed,
and an acceleration sensor for measuring components of the
gravitational acceleration exerted on the weighing scale. A memory
stores compensation factors with sets of components of the
gravitational acceleration, each of the first compensation factors
being a ratio between the true weight value of a material and an
apparent weight value of the material, which is assumed to be
measured by the weight measurer when the planar surface is inclined
at an angle. The weighing scale further includes a compensator that
refers to the memory for obtaining an appropriate compensation
factor corresponding to the components of the gravitational
acceleration currently being measured by the acceleration sensor.
The compensator compensates for, by the obtained compensation
factor, the apparent weight value of the object to be weighed
indicated by the weight data currently being output from the weight
measurer.
Inventors: |
Kenmochi; Masayuki;
(Daisen-shi, JP) |
Correspondence
Address: |
HOGAN & HARTSON LLP;IP GROUP, COLUMBIA SQUARE
555 THIRTEENTH STREET, N.W.
WASHINGTON
DC
20004
US
|
Assignee: |
TANITA Corporation
|
Family ID: |
39560891 |
Appl. No.: |
12/149099 |
Filed: |
April 25, 2008 |
Current U.S.
Class: |
73/1.08 |
Current CPC
Class: |
G01G 3/1414
20130101 |
Class at
Publication: |
73/1.08 |
International
Class: |
G01G 23/01 20060101
G01G023/01 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2007 |
JP |
2007-115123 |
Claims
1. A weighing scale comprising: a platform comprising a planar
surface on which an object to be weighed, having a weight, is
placed; a weight measurer for outputting weight data indicating an
apparent weight value of the object to be weighed on the planar
surface of the platform, the apparent weight value being affected
by inclination of the planar surface; an acceleration sensor for
measuring at least two components of the gravitational acceleration
exerted on the weighing scale in at least two directions that are
orthogonal to each other; and a first compensator which
compensates, on the basis of the at least two components of the
gravitational acceleration currently being measured by the
acceleration sensor, the apparent weight value of the object to be
weighed indicated by the weight data currently being output from
the weight measurer, thereby determining a compensated weight value
of the object to be weighed.
2. The weighing scale according to claim 1, further comprising a
memory for storing first compensation factors, each of the first
compensation factors being a ratio between a true weight value of a
material and an apparent weight value of the material which is
assumed to be measured by the weight measurer when the planar
surface is inclined at an angle, the first compensator referring to
the memory for obtaining a first compensation factor corresponding
to the components of the gravitational acceleration currently being
measured by the acceleration sensor, the first compensator
compensating, by the obtained first compensation factor, the
apparent weight value of the object to be weighed indicated by the
weight data currently being output from the weight measurer,
thereby determining a compensated weight value of the object to be
weighed.
3. The weighing scale according to claim 2, wherein the memory
stores the first compensation factors and sets of components of the
gravitational acceleration, each of the sets of components of the
gravitational acceleration having at least two components of the
gravitational acceleration that are assumed to be exerted on the
weighing scale in at least two orthogonal directions when the
planar surface is inclined at an angle, each of the first
compensation factors being associated in the memory with a set of
components of the gravitational acceleration that are assumed to be
exerted on the weighing scale when the planar surface is inclined
at the angle corresponding to the apparent weight value of the
material.
4. The weighing scale according to claim 3, wherein the first
compensator interpolates the first compensation factor
corresponding to the components of the gravitational acceleration
currently being measured by the acceleration sensor, on the basis
of the first compensation factors and sets of components of the
gravitational acceleration stored in the memory and the components
of the gravitational acceleration currently being measured by the
acceleration sensor.
5. The weighing scale according to claim 3, further comprising a
first compensation factor generator and a recorder, the first
compensation factor generator receiving, from the weight measurer,
weight data indicating the apparent weight value of the material on
the planar surface of the platform the weight measurer when the
planar surface is inclined at an angle, the first compensation
factor generator calculates a first compensation factor that is a
ratio between the true weight value of the material and the
apparent weight value of the material, the recorder recording the
first compensation factor calculated by the first compensation
factor generator with a set of components of the gravitational
acceleration measured by the acceleration sensor when the planar
surface is inclined at the angle at which the first compensation
factor generator receives, from the weight measurer, the weight
data indicating the apparent weight value of the material.
6. The weighing scale according to claim 2, wherein the memory
stores the first compensation factors and angles of inclination of
the planar surface, each of the first compensation factors being
associated in the memory with the angle of inclination of the
planar surface corresponding to the apparent weight value of the
material; the weighing scale further comprising an inclination
angle calculator for calculating a current angle of inclination of
the planar surface on the basis of the components of the
gravitational acceleration currently being measured by the
acceleration sensor; the first compensator referring to the memory
for obtaining a first compensation factor corresponding to the
current angle of inclination of the planar surface calculated by
the inclination angle calculator, the first compensator
compensating, by the obtained first compensation factor, the
apparent weight value of the object to be weighed indicated by the
weight data currently being output from the weight measurer,
thereby determining a compensated weight value of the object to be
weighed.
7. The weighing scale according to claim 6, wherein the first
compensator interpolates the first compensation factor
corresponding to the current angle of inclination of the planar
surface currently calculated by the inclination angle calculator,
on the basis of the first compensation factors and angles of
inclination of the planar surface stored in the memory and the
current angle of inclination of the planar surface currently
calculated by the inclination angle calculator.
8. The weighing scale according to claim 6, further comprising a
first compensation factor generator and a recorder, the first
compensation factor generator receiving, from the weight measurer,
weight data indicating the apparent weight value of the material on
the planar surface of the platform the weight measurer when the
planar surface is inclined at an angle, the first compensation
factor generator calculates a first compensation factor that is a
ratio between the true weight value of the material and the
apparent weight value of the material, the recorder recording the
first compensation factor calculated by the first compensation
factor generator with the angle calculated by the inclination angle
calculator at which the first compensation factor generator
receives, from the weight measurer, the weight data indicating the
apparent weight value of the material.
9. The weighing scale according to claim 1, wherein the memory
stores a reference gravitational acceleration at a reference point,
the weighing scale comprising: a second acceleration sensor
measuring three components of the gravitational acceleration
exerted on the weighing scale in three directions that are
orthogonal to one another; a gravitational acceleration calculator
for calculating an actual gravitational acceleration exerted on the
weighing scale that is the square root of the sum of the squares of
the three components of the gravitational acceleration measured by
the second acceleration sensor; and a second compensator for
calculating a second compensation factor that is a ratio between
the reference gravitational acceleration and the actual
gravitational acceleration, and for compensating, by the second
compensation factor, the compensated weight value determined by the
first compensator, thereby determining a second compensated weight
value of the object to be weighed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a weighing scale having a
platform on which objects to be weighed are placed, and having a
weight measurer for measuring the weights of the objects.
DESCRIPTION OF RELATED ART
[0002] There have been developed techniques for maintaining
platforms of weighing scales so as to be horizontal because if the
platform were inclined, the weight sensor (weight measurer) would
output an erroneous result due to the inclination, and such an
error often could not have been estimated in advance.
[0003] For example, JP 2005-49271A discloses a weighing scale
containing a spirit level therein. The user observes the spirit
level and adjusts the lengths of legs of the weighing scale,
whereby the weighing scale may be oriented so as to be
horizontal.
[0004] However, adjusting the scale so that it is level and
horizontal takes a substantial amount of time. Furthermore,
whenever the weighing scale is moved and is set up in another
location, this troublesome leveling and adjusting it so as to be
horizontal must be performed.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention provides a weighing scale
that can easily compensate for the errors in measured weights due
to inclination of the platform (inclination-induced error) so that
it is easier for users to set up the weighing scale.
[0006] In accordance with an aspect of the invention, there is
provided a platform including a planar surface on which an object
to be weighed, having a weight, is placed; a weight measurer for
outputting weight data indicating an apparent weight value of the
object to be weighed on the planar surface of the platform, the
apparent weight value being affected by inclination of the planar
surface; an acceleration sensor for measuring at least two
components of the gravitational acceleration exerted on the
weighing scale in at least two directions that are orthogonal to
each other; and a first compensator which compensates, on the basis
of the at least two components of the gravitational acceleration
currently being measured by the acceleration sensor, the apparent
weight value of the object to be weighed indicated by the weight
data currently being output from the weight measurer, thereby
determining a compensated weight value of the object to be
weighed.
[0007] With such a structure, the first compensator compensates the
apparent weight value of the object to be weighed indicated by the
weight data currently being output from the weight measurer, on the
basis of the at least two components of the gravitational
acceleration currently being measured by the acceleration sensor.
Therefore, the weighing scale automatically compensates for the
error of the measured weight due to inclination of the platform
(inclination-induced error) without users having to go through the
trouble of making the planar surface level and horizontal by
observing the spirit level, and determines the compensated and
precise weight value of the object being weighed. This is
convenient because the troublesome operations for orienting the
weighing scale horizontally can be avoided, even when the weighing
scale is moved and is set up in another location.
[0008] The weighing scale may further include a memory for storing
first compensation factors, each of the first compensation factors
being a ratio between a true weight value of a material and an
apparent weight value of the material which is assumed to be
measured by the weight measurer when the planar surface is inclined
at an angle, the first compensator referring to the memory for
obtaining a first compensation factor corresponding to the
components of the gravitational acceleration currently being
measured by the acceleration sensor, the first compensator
compensating, by the obtained first compensation factor, the
apparent weight value of the object to be weighed indicated by the
weight data currently being output from the weight measurer,
thereby determining a compensated weight value of the object to be
weighed. Therefore, the first compensator compensates the apparent
weight value of the object to be weighed, using the first
compensation factor that is the ratio between the true weight value
and the apparent weight value and corresponds to the current angle
of inclination of the planar surface. The weighing scale can
precisely determine the compensated weight value of the object
being weighed.
[0009] In an embodiment of the present invention, the memory may
store the first compensation factors and sets of components of the
gravitational acceleration, each of the sets of components of the
gravitational acceleration having at least two components of the
gravitational acceleration that are assumed to be exerted on the
weighing scale in at least two orthogonal directions when the
planar surface is inclined at an angle, each of the first
compensation factors being associated in the memory with a set of
components of the gravitational acceleration that are assumed to be
exerted on the weighing scale when the planar surface is inclined
at the angle corresponding to the apparent weight value of the
material. In this embodiment, it is easy for the first compensator
to obtain the first compensation factor corresponding to the
components of the gravitational acceleration currently being
measured since each first compensation factor is associated in the
memory with a set of components of the gravitational
acceleration.
[0010] In the weighing scale according to this embodiment of the
present invention, the memory may store a large number of the first
compensation factors and a large number of the sets of components
of the gravitational acceleration in order to compensate for any
errors caused by various angles of inclination of the platform.
[0011] However, preferably, the first compensator may interpolate
the first compensation factor corresponding to the components of
the gravitational acceleration currently being measured by the
acceleration sensor, on the basis of the first compensation factors
and sets of components of the gravitational acceleration stored in
the memory and the components of the gravitational acceleration
currently being measured by the acceleration sensor. Therefore, a
limited number of the first compensation factors and a limited
number of the sets of components of the gravitational acceleration
may be stored in the memory.
[0012] For the weighing scale according to this embodiment of the
present invention, the contents (first compensation factors and
sets of components of the gravitational acceleration) stored in the
memory may be measured or be determined at another machine, which
may be of the same type as in this aspect of the present invention.
The contents may be transferred from outside of the weighing scale
and be written into the memory.
[0013] However, preferably, the weighing scale further includes a
first compensation factor generator and a recorder, the first
compensation factor generator receiving, from the weight measurer,
weight data indicating the apparent weight value of the material on
the planar surface of the platform of the weight measurer when the
planar surface is inclined at an angle, the first compensation
factor generator calculates a first compensation factor that is a
ratio between the true weight value of the material and the
apparent weight value of the material, the recorder recording the
first compensation factor calculated by the first compensation
factor generator with a set of components of the gravitational
acceleration measured by the acceleration sensor when the planar
surface is inclined at the angle at which the first compensation
factor generator receives, from the weight measurer, the weight
data indicating the apparent weight value of the material. The
weight measurer of the weighing scale actually measures the
apparent weight value of a material, and the first compensation
factor generator calculates a first compensation factor on the
basis of the true weight value and the apparent weight value
actually measured by the weight measurer of the weighing scale.
Furthermore, the recorder records the calculated first compensation
factor with a set of components of the gravitational acceleration
actually measured by the acceleration sensor of the weighing scale.
Therefore, the instrumental error of the weight measurer and the
instrumental error of the acceleration sensor may be compensated
for in addition to the inclination-induced error.
[0014] In accordance with another embodiment of the invention, the
memory may store the first compensation factors and angles of
inclination of the planar surface, each of the first compensation
factors being associated in the memory with the angle of
inclination of the planar surface corresponding to the apparent
weight value of the material. The weighing scale further include an
inclination angle calculator for calculating a current angle of
inclination of the planar surface on the basis of the components of
the gravitational acceleration currently being measured by the
acceleration sensor. The first compensator refers to the memory for
obtaining a first compensation factor corresponding to the current
angle of inclination of the planar surface calculated by the
inclination angle calculator, the first compensator compensating,
by the obtained first compensation factor, the apparent weight
value of the object to be weighed indicated by the weight data
currently being output from the weight measurer, thereby
determining a compensated weight value of the object to be weighed.
In this embodiment, it is easy for the first compensator to obtain
the first compensation factor corresponding to the components of
the gravitational acceleration currently being measured since each
first compensation factor is associated in the memory with the
angle of inclination.
[0015] In the weighing scale according to this embodiment of the
present invention, the memory may store a large number of the first
compensation factors and a large number of the angles of
inclination in order to compensate for any errors caused by various
angles of inclination of the platform.
[0016] However, preferably, the first compensator may interpolate
the first compensation factor corresponding to the current angle of
inclination of the planar surface currently calculated by the
inclination angle calculator, on the basis of the first
compensation factors and angles of inclination of the planar
surface stored in the memory and the current angle of inclination
of the planar surface currently calculated by the inclination angle
calculator. In this embodiment, a limited number of the first
compensation factors and a limited number of the angles of
inclination may be stored in the memory.
[0017] For the weighing scale according to this embodiment of the
present invention, the contents (first compensation factors and
angles of inclination) stored in the memory might be measured or
determined at another machine, which may be of the same type as in
this aspect of the present invention. The contents might be
transferred from outside of the weighing scale and be written into
the memory.
[0018] However, preferably, the weighing scale further includes a
first compensation factor generator and a recorder, the first
compensation factor generator receiving, from the weight measurer,
weight data indicating the apparent weight value of the material on
the planar surface of the platform the weight measurer when the
planar surface is inclined at an angle, the first compensation
factor generator calculates a first compensation factor that is a
ratio between the true weight value of the material and the
apparent weight value of the material, the recorder recording the
first compensation factor calculated by the first compensation
factor generator with the angle calculated by the inclination angle
calculator at which the first compensation factor generator
receives, from the weight measurer, the weight data indicating the
apparent weight value of the material. In this embodiment, the
weight measurer of the weighing scale actually measures the
apparent weight value of a material, and the first compensation
factor generator calculates a first compensation factor on the
basis of the true weight value and the apparent weight value
actually measured by the weight measurer of the weighing scale.
Furthermore, the recorder records the calculated first compensation
factor with the angle calculated by the inclination angle
calculator on the basis of a set of components of the gravitational
acceleration actually measured by the acceleration sensor of the
weighing scale. Therefore, in accordance with this embodiment, the
instrumental error of the weight measurer and the instrumental
error of the acceleration sensor may be compensated for in addition
to the inclination-induced error.
[0019] In each embodiment of the present invention, the memory may
store a reference gravitational acceleration at a reference point,
the acceleration sensor measuring three components of the
gravitational acceleration exerted on the weighing scale in three
directions that are orthogonal to one another. The weighing scale
may further include: a second acceleration sensor measuring three
components of the gravitational acceleration exerted on the
weighing scale in three directions that are orthogonal to one
another; a gravitational acceleration calculator for calculating an
actual gravitational acceleration exerted on the weighing scale
that is the square root of the sum of the squares of the three
components of the gravitational acceleration measured by the second
acceleration sensor; and a second compensator for calculating a
second compensation factor that is a ratio between the reference
gravitational acceleration and the actual gravitational
acceleration, and for compensating, by the second compensation
factor, the compensated weight value determined by the first
compensator, thereby determining a second compensated weight value
of the object to be weighed.
[0020] Gravitational acceleration varies slightly depending on the
location on Earth, and therefore, the weight data output from the
weight measurer is affected by the gravitational error. The
gravitational error can be assumed for individual locations and can
be eliminated from the measured weight by the user setting the
weighing scale. However, according to the above-described
embodiment, the second compensator calculates the second
compensation factor on the basis of the reference gravitational
acceleration and the actual gravitational acceleration that is
calculated from three components of the gravitational acceleration
actually measured by the second acceleration sensor, and further
compensates for the compensated weight value. Therefore, the
gravitational error can be automatically subtracted out without the
user setting the weighing scale.
[0021] The second acceleration sensor may be the same as, or
different from, the acceleration sensor used for compensating for
the inclination-induced error.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] With reference to the accompanying drawings, various
embodiments of the present invention will be described hereinafter.
In the drawings:
[0023] FIG. 1A is a plane view showing a weighing scale of a first
embodiment according to the present invention;
[0024] FIG. 1B is a front view showing the weighing scale in FIG.
1A;
[0025] FIG. 2 is a functional block diagram showing functions of
the weighing scale in FIG. 1A;
[0026] FIG. 3 is a schematic diagram showing the principle of
measuring components of the gravitational acceleration by an
acceleration sensor in the weighing scale in FIG. 1A;
[0027] FIG. 4 is a table showing an example of contents of a
compensation table stored in a memory of the weighing scale in FIG.
1A;
[0028] FIG. 5 is a flowchart representing the flow of a measurement
process according to the first embodiment;
[0029] FIG. 6 is a flowchart representing the flow of a calibration
process according to the first embodiment;
[0030] FIG. 7 is a flowchart representing the flow of a measurement
process according to a second embodiment of the present
invention;
[0031] FIG. 8 is a flowchart representing the flow of a calibration
process according to the second embodiment;
[0032] FIG. 9 is a functional block diagram showing functions of a
weighing scale of a third embodiment according to the present
invention;
[0033] FIG. 10 is a flowchart representing the flow of a
measurement process according to the third embodiment;
[0034] FIG. 11 is a flowchart representing the flow of a
calibration process according to the third embodiment; and
[0035] FIG. 12 is a table showing an example of contents of another
compensation table in a modified embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
[0036] As shown in FIGS. 1A and 1B, a weighing scale 10A of a first
embodiment according to the present invention includes a casing or
housing 1 supported by a plurality of legs 11 on a support surface
(e.g. a floor), and a platform 2 including an upper planar surface
2a on which an object to be weighed is placed.
[0037] A weight measurer 130 is located within the housing 1. The
platform 2 is attached to the housing 1 in such a manner that the
weight measurer 130 measures the load, i.e., weight of the object
to be weighed on the planar surface 2a of the platform 2. The
weight measurer 130 may be a load cell or a weight sensor that
outputs weight data indicating the weight value of the object to be
weighed on the planar surface 2a of the platform 2.
[0038] An accelerometer, i.e., acceleration sensor 120 is mounted
on the platform 2. The acceleration sensor 120 is very sensitive
and appropriately calibrated, so that the acceleration sensor 120
can measure even components of the gravitational acceleration
(gravity acceleration) exerted on the platform 2. The acceleration
sensor 120 is, for example, but is not limited to, a
piezo-resistive semiconductor-based acceleration sensor, a
capacitive semiconductor-based acceleration sensor, or a thermal
acceleration sensor.
[0039] In an alternative embodiment, the acceleration sensor 120
may be mounted on another location in the weighing scale since the
weighing scale is not so large that the gravitational acceleration
exerted on the sensor 120 can be considered constant as far as the
sensor 120 is mounted on the weighing scale. Therefore, the
acceleration sensor 120 can measure components of the gravitational
acceleration exerted on the location to which the sensor 120 is
mounted, but the measured components are generally equal to those
exerted on the platform 2.
[0040] An electric power switch 3 is provided at a side surface of
the electric power switch 3 for turning on and off the power to the
weighing scale 10A. A display 140 is provided on the top wall of
the housing 1 for displaying suitable information, such as the
result of measurement (measured weight). The display 140 is, for
example, but is not limited to, an LCD (liquid crystal
display).
[0041] As shown in FIG. 2, the weighing scale 10A further includes
a memory 150 and a CPU (central processing unit) 110 that are
located in the housing 1. The CPU 110 conducts overall control of
the weighing scale 10A.
[0042] FIG. 3 is a schematic diagram showing the principle of the
measuring components of the gravitational acceleration by the
acceleration sensor 120. Let us assume that the acceleration sensor
120 is a triaxial type that can measure accelerations A.sub.x,
A.sub.y, and A.sub.z in the x, y, and z directions that are, of
course, orthogonal to one another. The acceleration sensor 120 is
secured to weighing scale so that the x and y axes of the
acceleration sensor 120 are parallel to the upper planar surface 2a
of the platform 2, the x axis is parallel to the lateral direction
of the platform 2, and the y axis is parallel to the
anteroposterior direction of the platform 2.
[0043] When the acceleration sensor 120 is in the static condition
(no dynamic load or force is being applied to the acceleration
sensor 120), only the gravitational acceleration (static
acceleration) is exerted on the acceleration sensor 120, and
therefore, the measured accelerations A.sub.x, A.sub.y, and A.sub.z
are the components of the gravitational acceleration in the x, y,
and z directions. The amounts of the components A.sub.x, A.sub.y,
and A.sub.z of the gravitational acceleration are related to the
inclination angles of the x, y, and z axes of the acceleration
sensor 120. More specifically, when the x axis of the acceleration
sensor 120 is inclined so as to intersect a horizontal plane A at
an angle .theta..sub.x (to intersect the Z axis (absolute vertical
axis) at an angle (90-.theta..sub.x) (degrees), the acceleration
sensor 120 measures the component of the gravitational acceleration
in the x direction, of which the amount A.sub.x is g times cos
(90-.theta..sub.x) where g is the gravitational acceleration. When
the y axis of the acceleration sensor 120 is inclined so as to
intersect the horizontal plane A at an angle .theta..sub.y (to
intersect the Z axis (absolute vertical axis) at an angle
(90-.theta..sub.y) (degrees), the acceleration sensor 120 measures
the component of the gravitational acceleration in the y direction,
of which the amount A.sub.y is g times cos (90-.theta..sub.y). When
the z axis of the acceleration sensor 120 is inclined so as to
intersect the Z axis (absolute vertical axis) at an angle
.theta..sub.z (degrees), the acceleration sensor 120 measures the
component of the gravitational acceleration in the z direction, of
which the amount A.sub.z is g times cos .theta..sub.z.
[0044] As described above, angles .theta..sub.x, .theta..sub.y and
.theta..sub.z are the inclination angles of the acceleration sensor
120. Angles .theta..sub.x, .theta..sub.y and .theta..sub.z are the
inclination angles of the upper planar surface 2a of the platform 2
since the acceleration sensor 120 is secured and oriented to the
platform 2 as described above.
[0045] In this embodiment, the outputs A.sub.x and A.sub.y from the
acceleration sensor 120 are utilized as will be described later.
Therefore, the acceleration sensor 120 need not necessarily be a
triaxial type, and it may be a biaxial type that can measure
accelerations A.sub.x and A.sub.y in this embodiment.
[0046] As shown in FIG. 2, the weight measurer 130 outputs weight
data M.sub.p indicating the weight value of an object to be weighed
on the planar surface 2a of the platform 2, but the measured weight
value is an apparent weight value affected by inclination of the
planar surface 2a. For example, if the upper planar surface 2a is
inclined at .theta..sub.x (but .theta..sub.y is zero degrees), the
weight data M.sub.p indicates an apparent value that is equal to W
times cos .theta..sub.x when W is the true weight of the object to
be weighed. If the upper planar surface 2a is inclined at
.theta..sub.y (but .theta..sub.x is zero degrees), the weight data
M.sub.p indicates an apparent value that is equal to W times cos
.theta..sub.y. If the upper planar surface 2a is inclined at
.theta..sub.x and .theta..sub.y, the weight data M.sub.p indicates
an apparent value affected by the angles .theta..sub.x and
.theta..sub.y.
[0047] The CPU 110 (first compensator) compensates for the apparent
weight value indicated by the weight data M.sub.p so as to exclude
inclination-induced error on the basis of a set of components of
the gravitational acceleration (A.sub.x and A.sub.y) measured by
the acceleration sensor 120. The CPU 110 thus determines a
compensated weight value of the object to be weighed, and it
generates compensated weight data M.sub.out1. The display 140 shows
the compensated weight value indicated by the compensated weight
data M.sub.out1.
[0048] For the compensation of the apparent weight value, the
memory 150 stores a compensation table TBL1 that will be referred
to by the CPU 110. The memory 150 is, for example, but is not
limited to, a ROM (read only memory). If the compensation table
TBL1 is written into the memory 150 at this weighing scale 10A, the
memory 150 is preferably an EPROM (erasable programmable read-only
memory).
[0049] As shown in FIG. 4, the compensation table TBL1 stores first
compensation factors k.sub.0 through k.sub.4 and sets of components
of the gravitational acceleration (A.sub.x and A.sub.y). In FIG. 4,
each number in brackets indicates angle .theta..sub.x or
.theta..sub.y that takes on values of 0, +1.5, and -1.5 degrees.
Each of the first compensation factors k.sub.0 through k.sub.4 is
the ratio between a true weight value of a material and an apparent
weight value of the material which is assumed to be measured by the
weight measurer 130 when the planar surface 2a of the platform 2 is
inclined at the angle resulting from angles .theta..sub.x and
.theta..sub.y. For example, the first compensation factors k.sub.0
is the ratio between the true weight value and the apparent weight
value when the upper planar surface 2a is not inclined (the value
of k.sub.0 is 1 if the weight measurer 130 is accurate). The first
compensation factors k.sub.1 is the ratio between the true weight
value and the apparent weight value when the upper planar surface
2a is inclined at angle .theta..sub.x, that is equal to +1.5
degrees, but angle .theta..sub.y is zero degrees. The first
compensation factors k.sub.4 is the ratio between the true weight
value and the apparent weight value when the upper planar surface
2a is inclined at angle .theta..sub.y that is equal to -1.5
degrees, but angle .theta..sub.x is zero degrees.
[0050] The true weight value and the apparent weight values may be
actually measured by the weight measurer 130 of this weighing scale
10A, but may also be measured by another device at another
location. The first compensation factor may be the ratio of the
apparent weight to the true weight, but may be the ratio of the
true weight to the apparent weight.
[0051] In the compensation table TBL1, each of the first
compensation factors k.sub.0 through k.sub.4 is associated with a
set of components of the gravitational acceleration (A.sub.x and
A.sub.y) that is assumed to be exerted on the weighing scale when
the planar surface 2a is inclined at the angle corresponding to the
apparent weight value. For example, factor k.sub.1 is associated
with a set of components A.sub.x[+1.5] and A.sub.y[0], whereas
factor k.sub.4 is associated with a set of components A.sub.x[0]
and A.sub.y[-1.5]. The components of the gravitational acceleration
(A.sub.x and A.sub.y) may be actually measured by the acceleration
sensor 120 of this weighing scale 10A, but may also be measured by
another accelerometer at another location.
[0052] With reference to FIG. 5, the flow of a measurement process
for measuring the weight of an object to be weighed in the weighing
scale 10A will be described next. The CPU 110 conducts the
measurement process according to a computer program (that is, a
measurement program). This program may be stored in the memory 150
or another suitable information recording medium (not shown).
[0053] The user turns on the power to the weighing scale 10A and
places an object to be weighed on the upper planar surface 2a of
the platform 2. Then, the measurement program runs so as to execute
the measurement process. In the measurement process, the CPU 110
obtains the weight data M.sub.p output from the weight measurer 130
and the components of the gravitational acceleration (A.sub.x and
A.sub.y) output from the acceleration sensor 120 at step SB1.
[0054] Next, the CPU 110 (first compensator) reads the contents
stored in the compensation table TBL1 of the memory 150 at step
SB3. At step SB5, the CPU 110 calculates a first compensation
factor k corresponding to the components of the gravitational
acceleration (A.sub.x and A.sub.y) that were currently measured by
the acceleration sensor 120 and were obtained at step SB1. For this
calculation, for example, interpolation may be used. More
specifically, the CPU 110 uses at least one interpolating formula
to estimate the subject first compensation factor k on the basis of
the first compensation factors k.sub.0 through k.sub.4 and sets of
components of the gravitational acceleration (A.sub.x[0],
A.sub.x[+1.5], and A.sub.x[-1.5]; and A.sub.y[0], A.sub.y[+1.5],
and A.sub.y[-1.5]) stored in the memory 150 and the current
components (A.sub.x and A.sub.y) of the gravitational acceleration
currently being measured by the acceleration sensor 120. For
example, if the current components (A.sub.x and A.sub.y) of the
gravitational acceleration are (A.sub.x1 and A.sub.y1) where
A.sub.x[0]<A.sub.x1<A.sub.x[+1.5] and A.sub.y1=A.sub.y[0],
the interpolation formula can be transformed into a simplified form
below.
k={k.sub.0.times.(A.sub.x[+1.5]--A.sub.x1)+k.sub.1.times.(A.sub.x1-A.sub-
.x[0])}+(A.sub.x[+1.5]-A.sub.x[0])
[0055] Then, the CPU 110 as the first compensator compensates by
the obtained first compensation factor k, the apparent weight value
of the object to be weighed indicated by the weight data M.sub.p
which was currently being output from the weight measurer and was
obtained at step SB1, thereby determining a compensated weight
value of the object to be weighed at step SB7. The CPU 110
generates compensated weight data M.sub.out1 and causes the display
140 to show the compensated weight value indicated by the
compensated weight data M.sub.out1. In this compensation, the
apparent weight value may be divided by the first compensation
factor when the first compensation factor is the ratio of the
apparent weight to the true weight, but the apparent weight value
may be multiplied by the first compensation factor when the first
compensation factor is the ratio of the true weight to the apparent
weight.
[0056] Thus, the weighing scale 10A automatically compensates for
the inclination-induced error without users having to go through
the trouble of making the planar surface level and horizontal by
observing the spirit level, and it determines the compensated and
precise weight value of the object to be weighed. This is
convenient since a troublesome operation for orienting the weighing
scale horizontally can be avoided even when the weighing scale is
moved and is set up at another location.
[0057] In an alternative embodiment, the memory 150 may store a
large number of the first compensation factors and a large number
of the sets of components of the gravitational acceleration in such
a manner that each compensation factor is associated in the memory
with a set of components of the gravitational acceleration. In this
alternative embodiment, the CPU may choose a first compensation
factor corresponding to the components of the gravitational
acceleration (A.sub.x and A.sub.y) currently measured by the
acceleration sensor 120 from among the many first compensation
factors stored in the memory 150.
[0058] However, in the first embodiment, the weighing scale 10A
uses the above-mentioned calculation for estimating the first
compensation factor which applies in the compensation as described
above. Consequently, a limited number of the first compensation
factors and a limited number of the sets of components of the
gravitational acceleration may be stored in the memory 150.
[0059] It is possible to envisage the contents (first compensation
factors and sets of components of the gravitational acceleration)
stored in the memory 150 might be measured or determined at another
machine, which may be of the same type as that of the present
invention. The contents might be transferred from outside of the
weighing scale 10A and be written into the memory 150.
[0060] However, in the weighing scale 10A according to the first
embodiment, the contents originate in this weighing scale 10A and
are recorded in the memory 150 in the weighing scale 10A itself in
order to eliminate instrumental errors, as will be described later.
This recording is preferably conducted in a calibration process at
the factory that manufactured the weighing scale 10A or in an
experimental laboratory before shipping the weighing scale 10A.
[0061] With reference to FIG. 6, the flow of a calibration process
for recording the first compensation factors and sets of components
of the gravitational acceleration will be described next. The CPU
110 conducts the calibration process according to a computer
program (that is, a calibration program). This program may be
stored in the memory 150 or another suitable information recording
medium (not shown).
[0062] In the calibration process, a material for which the true
weight value is known is used and is placed on the upper planar
surface 2a of the platform 2. The weighing scale 10A is located on
a support table by which the weighing scale 10A can be
inclined.
[0063] First, at step SA1, the CPU 110 waits for a notification
that is issued in response to the fact that the weighing scale 10A
including the upper planar surface 2a is horizontally oriented so
that (.theta..sub.x, .theta..sub.y)=(0, 0). The user should adjust
the support table to orient the platform 2 horizontally.
[0064] In the calibration process, inclination angles .theta..sub.x
and .theta..sub.y may be measured by an external device or
instrument. However, inclination angles .theta..sub.x and
.theta..sub.y may be calculated by the CPU 110 of the weighing
scale 10A on the basis of the components of the gravitational
acceleration (A.sub.x and A.sub.y) output from the acceleration
sensor 120 and displayed in the display 140. Angles .theta..sub.x
and .theta..sub.y can be calculated by the following formulae that
will be understood from the above description in conjunction with
FIG. 3.
90-.theta..sub.x=cos.sup.-1(A.sub.x/g)
90-.theta..sub.y=cos.sup.-1(A.sub.y/g)
where g is the gravitational acceleration, for example, the actual
gravitational acceleration if it is known or the standard
gravitational acceleration that is 9.80665 meters per second
squared established by the 3rd CGPM (General Conference on Weights
and Measures).
[0065] Once the angles (.theta..sub.x, .theta..sub.y) are adjusted
to be (0, 0), the user gives a notification to the CPU 110. Then,
the process proceeds to step SA3 where the CPU 110 (first
compensation factor generator) obtains the weight data M.sub.p
output from the weight measurer 130 and the components of the
gravitational acceleration (A.sub.x[0] and A.sub.y[0]) output from
the acceleration sensor 120. The CPU 110 calculates a first
compensation factor k.sub.0 that is the ratio between the true
weight value of the material and the apparent weight value of the
material indicated by the current weight data M.sub.p. The CPU 110
(as the recorder) records the first compensation factor k.sub.0 in
the compensation table TBL1 in such a manner that the first
compensation factor k.sub.0 is associated with the set of angles
(.theta..sub.x, .theta..sub.y) that is (0, 0). In addition, the CPU
110 records the components of the gravitational acceleration
(A.sub.x[0] and A.sub.y[0]) in the compensation table TBL1 in such
a manner that A.sub.x[0] is associated with angle .theta..sub.x
which is zero degrees and that A.sub.y[0] is associated with angle
.theta..sub.y which is zero degrees. As a result, the CPU 110
records the first compensation factor k.sub.0 with a set of
components of the gravitational acceleration (A.sub.x[0] and
A.sub.y[0]) measured by the acceleration sensor 120 when the planar
surface 2a is oriented horizontally.
[0066] Subsequently, at step SA5, the CPU 110 waits for a
notification that is issued in response to the fact that the
weighing scale 10A including the upper planar surface 2a is
inclined so that (.theta..sub.x, .theta..sub.y)=(+1.5, 0)
(degrees). The user should adjust the support table so that
(.theta..sub.x, .theta..sub.y)=(+1.5, 0) (degrees).
[0067] Once the angles (.theta..sub.x, .theta..sub.y) are adjusted
to be (+1.5, 0), the user gives a notification to the CPU 110.
Then, the process proceeds to step SA7 in which the CPU 110 (first
compensation factor generator) obtains the weight data M.sub.p
output from the weight measurer 130 and the components of the
gravitational acceleration (A.sub.x[+1.5] and A.sub.y[0]) output
from the acceleration sensor 120. The CPU 110 calculates a first
compensation factor k.sub.1 that is the ratio between the true
weight value of the material and the apparent weight value of the
material indicated by the current weight data M.sub.p. The CPU 110
(as the recorder) records the first compensation factor k in the
compensation table TBL1 in such a manner that the first
compensation factor k.sub.1 is associated with the set of angles
(.theta..sub.x, .theta..sub.y) that is (+1.5, 0). In addition, the
CPU 110 records the component of the gravitational acceleration
A.sub.x[+1.5] in the compensation table TBL1 in such a manner that
A.sub.x[+1.5] is associated with angle .theta..sub.x, which is +1.5
degrees. The other component A.sub.y[0] has been recorded in the
compensation table TBL1 appropriately since it was written at step
SA3. As a result, the CPU 110 records the first compensation factor
k.sub.1 with a set of components of the gravitational acceleration
(A.sub.x[+1.5] and A.sub.y[0]) measured by the acceleration sensor
120 when the planar surface 2a is inclined so that (.theta..sub.x,
.theta..sub.y)=(+1.5, 0) (degrees).
[0068] Subsequently, at step SA9, the CPU 110 waits for a
notification that is issued in response to the fact that the
weighing scale 10A including the upper planar surface 2a is
inclined so that (.theta..sub.x, .theta..sub.y)=(0, +1.5)
(degrees). The user should adjust the support table so that
(.theta..sub.x, .theta..sub.y)=(0, +1.5) (degrees).
[0069] Once the angles (.theta..sub.x, .theta..sub.y) are adjusted
to be (0, +1.5), the user gives a notification to the CPU 110.
Then, the process proceeds to step SA11 in which the CPU 110 (first
compensation factor generator) obtains the weight data M.sub.p
output from the weight measurer 130 and the components of the
gravitational acceleration (A.sub.x[0] and A.sub.y[+1.5]) output
from the acceleration sensor 120. The CPU 110 calculates a first
compensation factor k.sub.2 that is the ratio between the true
weight value of the material and the apparent weight value of the
material indicated by the current weight data M.sub.p. The CPU 110
(as the recorder) records the first compensation factor k.sub.2 in
the compensation table TBL1 in such a manner that the first
compensation factor k.sub.2 is associated with the set of angles
(.theta..sub.x, .theta..sub.y) that is (0, +1.5). In addition, the
CPU 110 records the component of the gravitational acceleration
A.sub.y[+1.5] in the compensation table TBL1 in such a manner that
A.sub.y[+1.5] is associated with angle .theta..sub.y, which is +1.5
degrees. The other component A.sub.x[0] has been recorded in the
compensation table TBL1 appropriately since it was written at step
SA3. As a result, the CPU 110 records the first compensation factor
k.sub.2 with a set of components of the gravitational acceleration
(A.sub.x[0] and A.sub.y[+1.5]) measured by the acceleration sensor
120 when the planar surface 2a is inclined so that (.theta..sub.x,
.theta..sub.y)=(0, +1.5) (degrees).
[0070] Similarly, by steps SA13 and SA15, another compensation
factor k.sub.3 is calculated and recorded in the compensation table
TBL1 in such a manner that the first compensation factor k.sub.3 is
associated with the set of angles (.theta..sub.x, .theta..sub.y)
that is (-1.5, 0) and with a set of components of the gravitational
acceleration (A.sub.x[-1.5] and A.sub.y[0]). By steps SA17 and
SA19, another compensation factor k.sub.4 is calculated and
recorded in the compensation table TBL1 in such a manner that the
first compensation factor k.sub.4 is associated with the set of
angles (0%, .theta..sub.y) that is (0, -1.5) and with a set of
components of the gravitational acceleration (A.sub.x[0] and
A.sub.y[-1.5]). Thus, the contents of the compensation table TBL1
in the memory 150 are completed as shown in FIG. 4 before shipping
the weighing scale 10A from the factory or the experimental
laboratory.
[0071] In weighing scales, there may be instrumental errors in
weight data M.sub.p resulting from production errors, etc., of the
weight measurers 130. Consequently, there is no guarantee that
multiple units of the weight measurers 130 of the same type will
each output the same measurements under the same conditions. Each
of the weight values indicated by the weight data M.sub.p involves
an instrumental error in addition to the inclination-induced error.
In this embodiment, the weight measurer 130 of the weighing scale
10A actually measures the apparent weight value of a material, and
the CPU 110 calculates the first compensation factor on the basis
of the true weight value and the apparent weight value actually
measured by the weight measurer 130 of the weighing scale 10A.
Therefore, by virtue of this embodiment, the instrumental error of
the weight measurer 130 may be compensated for in addition to the
inclination-induced error.
[0072] Furthermore, there may be instrumental errors in outputs of
acceleration sensor 120 resulting from production errors, etc., of
the acceleration sensors 120. Consequently, there is no guarantee
that multiple units of the acceleration sensors 120 of the same
type will each output the same measurements under the same
conditions. Each components of the gravitational acceleration
(A.sub.x and A.sub.y) measured by the acceleration sensor 120
involves an instrumental error, in addition to the
inclination-induced error. In the calibration process of this
embodiment, the CPU 110 records the calculated first compensation
factor with a set of components of the gravitational acceleration
(A.sub.x and A.sub.y) actually measured by the acceleration sensor
120 of the weighing scale 10A, which also measures components of
the gravitational acceleration in the measurement process.
Therefore, in accordance with this embodiment, the instrumental
error of the acceleration sensor 120 may be compensated for in
addition to the inclination-induced error.
Second Embodiment
[0073] A weighing scale of a second embodiment of the present
invention includes structures that are the same as those in the
first embodiment described in conjunction with FIGS. 1 to 3.
Therefore, the same reference symbols in the drawings for the first
embodiment are applied to corresponding parts in the second
embodiment.
[0074] The compensation table TBL1, for which the contents have
been described in conjunction with FIG. 4, is also stored in the
memory 150 in the second embodiment. However, it is not necessary
that the components of the gravitational acceleration (A.sub.x[0],
A.sub.x[+1.5], and A.sub.x[-1.5]; and A.sub.y[0], A.sub.y[+1.5],
and A.sub.y[-1.5]) be stored in the compensation table TBL1.
Referring back to FIG. 4, the compensation table TBL1 in the memory
150 stores first compensation factors k.sub.0 through k.sub.4 and
sets of components of the gravitational acceleration (A.sub.x and
A.sub.y). Each of the first compensation factors k.sub.0 through
k.sub.4 is the ratio between a true weight value of a material and
an apparent weight value of the material which is assumed to be
measured by the weight measurer 130 when the planar surface 2a of
the platform 2 is inclined at the angle resulting from angles
.theta..sub.x and .theta..sub.y.
[0075] In the compensation table TBL1, each of the first
compensation factors k.sub.0 through k.sub.4 is associated with the
angle of inclination of the upper planar surface 2a corresponding
to the apparent weight value. For example, factor k.sub.1 is
associated with the angle resulting from the fact that angle
.theta..sub.x is +1.5 degrees and .theta..sub.y is zero degrees,
whereas factor k.sub.4 is associated with a set of angles
(.theta..sub.x, .theta..sub.y) that are (0, -1.5).
[0076] With reference to FIG. 7, the flow of a measurement process
for measuring the weight of an object to be weighed in the weighing
scale 10A of the second embodiment will be described next. The CPU
110 conducts the measurement process according to a computer
program (that is, a measurement program). This program may be
stored in the memory 150 or another suitable information recording
medium (not shown).
[0077] The user turns on the power to the weighing scale 10A and
places an object to be weighed on the upper planar surface 2a of
the platform 2. Then, the measurement program runs so as to execute
the measurement process. In the measurement process, the CPU 110
obtains the weight data M.sub.p output from the weight measurer 130
and the components of the gravitational acceleration (A.sub.x and
A.sub.y) output from the acceleration sensor 120 at step SB11.
[0078] Next, at step SB12, the CPU 110 (as an inclination angle
calculator) calculates the current angles of inclination
(.theta..sub.x and .theta..sub.y) of the planar surface 2a of the
platform 2 on the basis of the components of the gravitational
acceleration (A.sub.x and A.sub.y) currently measured by the
acceleration sensor 120. It should be noted that angles
.theta..sub.x and .theta..sub.y can be calculated by the following
formulae as described above.
90-.theta..sub.x=cos.sup.-1(A.sub.x/g)
90-.theta..sub.y=cos.sup.-1(A.sub.y/g)
[0079] Next, the CPU 110 (first compensator) reads the contents
stored in the compensation table TBL1 of the memory 150 at step
SB13. At step SB16, the CPU 110 calculates a first compensation
factor k corresponding to the current angles of inclination
(.theta..sub.x and .theta..sub.y) of the planar surface 2a that
were currently calculated at step SB12. For this calculation, for
example, interpolation may be used. More specifically, the CPU 110
uses at least one interpolating formula to estimate the subject
first compensation factor k on the basis of the first compensation
factors k.sub.0 through k.sub.4 and sets of angles of inclination
(where .theta..sub.x=0, +1.5, or -1.5; and .theta..sub.y=0, +1.5,
or -1.5) stored in the memory 150 and the current angles of
inclination (.theta..sub.x and .theta..sub.y) currently calculated
by the CPU 110.
[0080] Then, the CPU 110 as the first compensator compensates, by
the obtained first compensation factor k, the apparent weight value
of the object to be weighed indicated by the weight data M.sub.p
which was currently output from the weight measurer and was
obtained at step SB11 in a manner similar to that in the first
embodiment, thereby determining a compensated weight value of the
object to be weighed at step SB17. The CPU 110 generates
compensated weight data M.sub.out1 and causes the display 140 to
show the compensated weight value indicated by the compensated
weight data M.sub.out1.
[0081] Thus, the weighing scale 10A automatically compensates for
the inclination-induced error without users having to go through
the trouble of making the planar surface level and horizontal by
observing the spirit level, and it determines the compensated and
precise weight value of the object to be weighed. This is
convenient since a troublesome operation for orienting the weighing
scale horizontally can be avoided even when the weighing scale is
moved and is set up at another location.
[0082] In an alternative embodiment, the memory 150 may store a
large number of the first compensation factors and a large number
of the angles of inclination in such a manner that each
compensation factor is associated in the memory with a set of the
angles of inclination. In this alternative embodiment, the CPU may
choose a first compensation factor corresponding to the angles of
inclination currently calculated from among the many first
compensation factors stored in the memory 150.
[0083] However, in the second embodiment, the weighing scale 10A
uses the above-mentioned calculation for estimating the first
compensation factor that applies in the compensation as described
above. Consequently, a limited number of the first compensation
factors and a limited number of the sets of angles may be stored in
the memory 150.
[0084] It is possible to conceive of the contents (first
compensation factors and sets of angles of inclination) stored in
the memory 150 might be measured or determined at another machine,
which may be of the same type as that of the present invention. The
contents might be transferred from outside of the weighing scale
10A and be written into the memory 150.
[0085] However, in the weighing scale 10A according to the second
embodiment, the contents originate in this weighing scale 10A and
are recorded in the memory 150 in the weighing scale 10A itself in
order to eliminate instrumental errors, as will be described later.
This recording is preferably conducted in a calibration process at
the factory that manufactured the weighing scale 10A or in an
experimental laboratory before shipping the weighing scale 10A. The
calibration process in the second embodiment may be the same as
that described with reference to FIG. 6 in conjunction with the
first embodiment, but it may also be different from that in the
first embodiment, as described below.
[0086] With reference to FIG. 8, the flow of a calibration process
for recording the first compensation factors and sets of sets of
angles of inclination in the second embodiment will be described
next. The CPU 110 conducts the calibration process according to a
computer program (that is, a calibration program) in a manner
similar to that in the first embodiment.
[0087] FIG. 8 is similar to FIG. 6, but it differs from FIG. 6 of
the first embodiment in that steps SA3, SA7, SA11, SA15, and SA19
are replaced by SA103, SA107, SA111, SA115, and SA119.
[0088] At step SA103, the CPU 110 (first compensation factor
generator) obtains the weight data M.sub.p output from the weight
measurer 130. The CPU 110 calculates a first compensation factor
k.sub.0 that is the ratio between the true weight value of the
material and the apparent weight value of the material indicated by
the current weight data M.sub.p. The CPU 110 (as the recorder)
records the first compensation factor k.sub.0 in the compensation
table TBL1 in such a manner that the first compensation factor
k.sub.0 is associated with the set of angles (.theta..sub.x,
.theta..sub.y) that is (0, 0).
[0089] At step SA107, the CPU 110 (first compensation factor
generator) obtains the weight data M.sub.p output from the weight
measurer 130. The CPU 110 calculates a first compensation factor k,
that is the ratio between the true weight value of the material and
the apparent weight value of the material indicated by the current
weight data M.sub.p. The CPU 110 (as the recorder) records the
first compensation factor k.sub.1 in the compensation table TBL1 in
such a manner that the first compensation factor k.sub.1 is
associated with the set of angles (.theta..sub.x,
.theta..sub.y).
[0090] At step SA111, the CPU 110 (first compensation factor
generator) obtains the weight data M.sub.p output from the weight
measurer 130. The CPU 110 calculates a first compensation factor
k.sub.2 that is the ratio between the true weight value of the
material and the apparent weight value of the material indicated by
the current weight data M.sub.p. The CPU 110 (as the recorder)
records the first compensation factor k.sub.2 in the compensation
table TBL1 in such a manner that the first compensation factor
k.sub.2 is associated with the set of angles (.theta..sub.x,
.theta..sub.y) that is (0, +1.5).
[0091] Similarly, by steps SA13 and SA115, another compensation
factor k.sub.3 is calculated and recorded in the compensation table
TBL1 in such a manner that the first compensation factor k.sub.3 is
associated with the set of angles (.theta..sub.x, .theta..sub.y)
that is (-1.5, 0). By steps SA17 and SA119, another compensation
factor k.sub.4 is calculated and recorded in the compensation table
TBL1 in such a manner that the first compensation factor k.sub.4 is
associated with the set of angles (.theta..sub.x, .theta..sub.y)
that is (0, -1.5). Thus, the contents of the compensation table
TBL1 in the memory 150 are completed before shipping the weighing
scale 10A from the factory or the experimental laboratory.
[0092] In this embodiment, the weight measurer 130 of the weighing
scale 10A actually measures the apparent weight value of a
material, and the CPU 110 calculates the first compensation factor
on the basis of the true weight value and the apparent weight value
actually measured by the weight measurer 130 of the weighing scale
10A. Therefore, by virtue of this embodiment, the instrumental
error of the weight measurer 130 may be compensated for in addition
to the inclination-induced error.
[0093] Furthermore, in the calibration process of this embodiment,
the CPU 110 records the calculated first compensation factor with a
set of angles calculated on the basis of a set of components of the
gravitational acceleration (A.sub.x and A.sub.y) actually measured
by the acceleration sensor 120 of the weighing scale 10A, which
also measures components of the gravitational acceleration in the
measurement process. Therefore, in accordance with this embodiment,
the instrumental error of the acceleration sensor 120 may be
compensated for in addition to the inclination-induced error.
Third Embodiment
[0094] Next, with reference to FIG. 9, a third embodiment of the
present invention will be described. In the third embodiment, the
gravitational error resulting from location-dependent differences
in gravitational acceleration can be excluded automatically. In
FIG. 9, the same symbols are used to designate elements that are
substantially the same as in FIG. 1, and these elements will not be
described in detail.
[0095] As shown in FIG. 9, the weighing scale 10B in the third
embodiment includes a second acceleration sensor 120b of a triaxial
type that can measure accelerations A.sub.x, A.sub.y, and A.sub.z
in the x, y, and z directions. In a manner similar to that in the
first and second embodiments, on the basis of the components of the
gravitational acceleration (A.sub.x and A.sub.y), the
inclination-induced error can be eliminated in the third
embodiment. In addition, the weighing scale 10B calculates the
actual gravitational acceleration exerted on the weighing scale on
the basis of the three components of the gravitational acceleration
(A.sub.x, A.sub.y, and A.sub.z) actually measured by the
acceleration sensor 120b. The actual gravitational acceleration
thus calculated is used for compensating for the gravitational
error.
[0096] More specifically, the actual gravitational acceleration
g.sub.a exerted on the weighing scale is the square root of the sum
of the squares of the three components of the gravitational
acceleration (A.sub.x, A.sub.y, and A.sub.z) measured by the
acceleration sensor 120b as represented in the formula below.
g.sub.a=(A.sub.x+A.sub.y.sup.2+A.sub.z.sup.2).sup.1/2
[0097] In this embodiment, the second acceleration sensor 120b is
used for measuring two components of the gravitational acceleration
(A.sub.x and A.sub.y) to compensate for the inclination-induced
error, and for measuring three components of the gravitational
acceleration (A.sub.x, A.sub.y, and A.sub.z) to calculate the
actual gravitational acceleration. In an alternative embodiment,
two acceleration sensors may be used for these two purposes,
respectively.
[0098] The weighing scale 10B further includes a memory 150b that
stores the compensation table TBL1 that has been described in
conjunction with the first and second embodiments. In addition, the
memory 150b stores a reference gravitational acceleration G.sub.r
at a reference point. The reference gravitational acceleration
G.sub.r may be the standard gravitational acceleration that is
9.80665 meters per second squared at a location at sea-level at
latitude 45 degrees north. However, in this embodiment, the
reference gravitational acceleration G.sub.r is determined on the
basis of three components of the gravitational acceleration
measured by the acceleration sensor 120b in a calibration process
conducted at the factory that manufactured the weighing scale 10A
or in an experimental laboratory. The reference gravitational
acceleration G.sub.r is calculated as follows:
G.sub.r=(A.sub.xr.sup.2+A.sub.yr.sup.2+A.sub.zr.sup.2).sup.1/2
in which A.sub.xr, A.sub.yr, and A.sub.zr are three components of
the gravitational acceleration measured by the acceleration sensor
120b at the reference point.
[0099] The apparent weight value of an object to be weighed on the
platform 2 that is indicated by the weight data M.sub.p output from
the weight measurer 130 is affected by the gravitational error.
This is because gravitational acceleration varies slightly
depending on location on the Earth. For example, it varies with
latitude, longitude, elevation, and subsurface density. The
gravitational error can be assumed for individual locations and can
be eliminated from the measured weight in accordance with a user
setting of the weighing scale. However, whenever the weighing scale
is moved and is set up at another location, this setting was
previously necessary to achieve accurate measurements. In order to
avoid this easily overlooked and troublesome setting, in this
embodiment, the weight value that originated from the weight
measurer 130 is corrected for by the ratio between the reference
gravitational acceleration G.sub.r and the actual gravitational
acceleration g.sub.a at the location at which the weighing scale
10B is to be used. Therefore, the gravitational error can be
automatically subtracted without a user setting the weighing scale,
even when the weighing scale 10B is used at different
locations.
[0100] FIG. 10 is a flowchart representing the flow of a
measurement process for measuring the weight of an object to be
weighed according to the third embodiment. The CPU 110 conducts the
measurement process according to a computer program (that is, a
measurement program). This program may be stored in the memory 150b
or another suitable information recording medium (not shown).
[0101] In a manner similar to that of the measurement process of
the first embodiment, when the user turns on the power to the
weighing scale 10A and places an object to be weighed on the upper
planar surface 2a of the platform 2, the measurement program runs
so as to execute the measurement process. At step SBb1, the CPU 110
obtains the weight data M.sub.p output from the weight measurer 130
and three components of the gravitational acceleration (A.sub.x,
A.sub.y, and A.sub.z) output from the acceleration sensor 120.
Then, in a manner similar to that of the measurement process of the
first embodiment, the process proceeds to steps SB3 through SB7,
whereby the CPU 110 compensates for the inclination-induced error
and determines a compensated weight value of the object to be
weighed, but this compensated weight value will not be displayed on
the display 140.
[0102] Thereafter, at step SBb9, the CPU 110 serves as a
gravitational acceleration calculator for calculating the actual
gravitational acceleration g.sub.a exerted on the weighing scale,
which is the square root of the sum of the squares of the three
components of the gravitational acceleration (A.sub.x, A.sub.y, and
A.sub.z) measured by the acceleration sensor 120. This actual
gravitational acceleration g.sub.a is the actual gravitational
acceleration at this measurement location.
[0103] At step SBb11, the CPU 110 serves as a second compensator
for calculating a second compensation factor that is the ratio
between the reference gravitational acceleration G.sub.r stored in
the memory 150b and the actual gravitational acceleration g.sub.a
at the measurement location. The second compensation factor may be
calculated as G.sub.r/g.sub.a or g.sub.a/G.sub.r. Then, the CPU 110
(second compensator) compensates, by the second compensation
factor, the compensated weight value determined at step SB7,
thereby determining a second compensated weight value of the object
to be weighed. The CPU 110 generates second compensated weight data
M.sub.out2 indicating the compensated weight value and causes the
display 140 to show the second compensated weight value indicated
by the second compensated weight data M.sub.out2. In this
compensation, the first compensated weight value may be multiplied
by the second compensation factor when the second compensation
factor is G.sub.r/g, but the first compensated weight value may be
divided by the second compensation factor when the second
compensation factor is g.sub.a/G.sub.r. Thus, the weighing scale
10A automatically conducts the measurement process including the
inclination compensation and the gravity compensation without the
process being troublesome for the user.
[0104] FIG. 11 is a flowchart representing the flow of a
calibration process according to the third embodiment. The CPU 110
conducts the calibration process according to a computer program
(that is, a calibration program). This program may be stored in the
memory 150b or another suitable information recording medium (not
shown).
[0105] In a manner similar to that of the calibration process of
the first embodiment, the process proceeds to steps SA1 through
SA19, whereby the contents of the compensation table TBL1 in the
memory 150b are completed at the factory or the experimental
laboratory.
[0106] Thereafter, at step SAb20, the CPU 110 obtains the three
components of the gravitational acceleration (A.sub.x, A.sub.y,
A.sub.z) simultaneously measured by the acceleration sensor 120. At
step SAb21, the CPU 110 serves as a reference gravitational
acceleration calculator for calculating the reference gravitational
acceleration G.sub.r. More specifically, the reference
gravitational acceleration G.sub.r is the square root of the sum of
the squares of the three components of the gravitational
acceleration (A.sub.x, A.sub.y, A.sub.z). It should be noted the
components (A.sub.x, A.sub.y, A.sub.z) at this stage are three
components of the reference gravitational acceleration (A.sub.xr,
A.sub.yr, A.sub.zr). Thus, the contents of the compensation table
TBL1 in the memory 150b are completed and the reference
gravitational acceleration G.sub.r is stored in the memory 150b
before shipping the weighing scale 10A from the factory or the
experimental laboratory.
[0107] As will be understood from the above description, in
addition to the advantages of the first embodiment, the third
embodiment may have an advantage that the gravity compensation can
be achieved automatically without the process being troublesome for
the user.
[0108] Modifications and Alterations
[0109] In the third embodiment, the calibration process includes
the calculation of the reference gravitational acceleration
G.sub.r. However, the calibration process and the calculation of
the reference gravitational acceleration G.sub.r may be conducted
in accordance with different computer programs, respectively.
[0110] As described above, the third embodiment is a modification
of the first embodiment. However, the same modification can be
applied to the second embodiment as well.
[0111] The third embodiment employs the inclination compensation
and the gravity compensation. However, it is possible to have the
weighing scale conduct the above-described gravity compensation,
but not conduct the inclination compensation.
[0112] FIG. 12 is a table showing an example of contents of another
compensation table TBL1a in a modified embodiment. In the
compensation table TBL1 shown in FIG. 4, only the five first
compensation factors k.sub.0 through k.sub.4 are stored. The
compensation table TBL1a shown in FIG. 7 stores four additional
first compensation factors k.sub.5 through k.sub.8. The factor
k.sub.5 corresponds to the set of angles (.theta..sub.x,
.theta..sub.y) that is (+1.5, +1.5). The factor k.sub.6 corresponds
to the set of angles (.theta..sub.x, .theta..sub.y) that is (+1.5,
-1.5). The factor k.sub.7 corresponds to the set of angles
(.theta..sub.x, .theta..sub.y) that is (-1.5, +1.5). The factor
k.sub.8 corresponds to the set of angles (.theta..sub.x,
.theta..sub.y) that is (-1.5, -1.5).
[0113] The compensation table TBL1a can be used instead of the
compensation table TBL1 in the first through third embodiments.
However, it is not necessary that the components of the
gravitational acceleration (A.sub.x[0], A.sub.x[+10.5], and
A.sub.x[-1.5]; and A.sub.y[0], A.sub.y[+1.5], and A.sub.y[-1.5]) be
stored in the compensation table TBL1 as in the second embodiment
and modifications of the second embodiment. By using the
compensation table TBL1a, it is possible to the improve accuracy of
the interpolation.
[0114] Other suitable modifications may be adopted for improving
the accuracy of interpolation. For example, the compensation table
may store more compensation factors corresponding to more sets of
angles (.theta..sub.x, .theta..sub.y) in which each of
.theta..sub.x, and .theta..sub.y can take intermediate values
between zero and +1.5 and between zero and -1.5.
[0115] In each of the above-described embodiments, the CPU 110 of
the weighing scale executes the calibration process for completing
the compensation table (and for calculating the reference
gravitational acceleration G.sub.r). However, it is possible for
another processing machine to be connected to the weight measurer
130 so as to perceive the true weight value output from the weight
measurer 130, and this processing machine calculates each first
compensation factor k on the basis of the output from the weight
measurer 130 and the true weight value. The processing machine may
also be connected to the acceleration sensor 120 so as to perceive
the components of the gravitational acceleration output from the
acceleration sensor 120. In this case, the processing machine can
complete the contents of the compensation table and can calculate
the reference gravitational acceleration G.sub.r. These data can be
transferred from the processing machine to the weighing scale and
be written into the memory. Although these data are calculated at
an external processing machine, they originated from the weighing
scale per se, and they contribute to the reduction in instrumental
errors.
[0116] In each of the above-described embodiments, the components
of the gravitational acceleration (A.sub.x and A.sub.y) output from
the acceleration sensor 120 are measured so as to be used as the
bases for determining the current first compensation factor that is
used for compensating the inclination-induced error in the
measurement process. However, it is not intended to so limit the
present invention. Alternatively, the components (A.sub.x and
A.sub.z) or (A.sub.y and A.sub.z) may be measured to be utilized
for determining the current first compensation factor. This is
because A.sub.y is a function of A.sub.x and A.sub.z, and A.sub.x
is also a function of A.sub.y and A.sub.z by the following formula
when the gravitational acceleration g.sub.a is considered to be a
known constant.
g.sub.a=(A.sub.x.sup.2+A.sub.y.sup.2+A.sub.z.sup.2).sup.1/2
* * * * *